Superheater



Aug. 30, 1966 w. N. M COY ETAL 3,269,368

SUPERHEATER Filed April 14, 1964 2 Sheets-Sheet l COMBUSTION SUPPORTING GAS INVENTORS.

N. McCOY .4 I'TOR NEYJ.

SUPERHEATER 2 Sheets-Sheet 2 Filed April 14, 1964 3 mm N J TEHiJ m l. 0v M D. mm m 3 LE m WIU United States Patent 3,269,368 SUPERHEATER Wiiliam N. McCoy and James D. Bell, Weirton, W. Va., assignors to National Steel Corporation, a corporation of Delaware Filed Apr. 14, 1964, Ser. No. 359,572 8 Claims. ((1 122-479) This invention is concerned with superheater structure and control and, more particularly, independent superheater structure and control apparatus providing rapidresponse temperature control for fluids with selected temperature and/ or selected pressure requirements.

The need for development of special process fluid heating has long been felt in the ant. Conventional vapor generator and superheater art provides no methods of operation or apparatus which will give rapid-response temperature control substantially unaffected by flow demand within the operating range.

The superheaters of the prior art, regardless of type, have depended largely upon flow control of combustants for heat control. Typical examples are shown and described in the Babcock and Wilcox text, Steam-Its Generation and Use, 37th Edition, Second Printing, 1955, page 132. Such superheaters are not adequate where the ability to select, at random, temperatures for a process with or without varying flow demand is required. It is a primary objective of this invention to provide superheater methods of operation, control, and superheater structure suitable for process applications where rapid response and selected temperature control are essential, with or without varying flow demand.

Details of the present invention will be described with reference to the accompanying drawings wherein:

FIGURE 1 is a schematic view, partially in section, of apparatus embodying the invention;

FIGURE 2 is a schematic view, partially in section, of apparatus embodying the invention;

FIGURE 3 is an enlarged view of a portion of the apparatus of FIGURES 1 and 2; and

FIGURE 4 is a schematic view, partially in section, of apparatus embodying the invention.

In these drawings, like numerals have been used to designate like parts where appropriate in the various figures.

The longitudinally extended independent superheater of FIGURE 1 includes a heating chamber 12, fuel burner 14, and flues In and 18. A helical coil is disposed within the heating chamber 12 with convolutions of coil 20 defining a cylindrical configuration having a longitudinal axis which is substantially coextensive with that of the heating chamber 12.

Fluid to be heated is introduced at the fluid inlet 22 of coil 20 and delivered at fluid outlet 24. Fuel and the combustion supporting gas are fed into the heating chamber 12 via fuel line 23 and combustion supporting gas line 25, respectively.

Gases of combustion discharged from fuel burner 14 travel along the longitudinal axis within the cylinder formed by the convolutions of coil 20. At the fluid outlet end of heating chamber 12, the gases of combustion are directed radially outwardly, as indicated by the flow arrows, and then in substantially counterflow relationship. Gases of combustion are discharged from the heating chamber through flues 16 and 18. It should be noted that the flue discharges are located at the fluid inlet end of the heating chamber 12 and that no damper control is provided. As will be seen from the description to follow, a constant volume of combustion supporting gas, such as air or oxygen enriched air, is provided and, with control of fuel supply, plays an important role in pro- 'ice ducing the rapid-response characteristics not found in the prior art.

The invention provides method and apparatus for operating the separately fired superheater described in in FIGURE 1 to provide rapid-response fluid delivery at selected temperature. Temperature selection and rapid response are available with constant or varying flow demands. To accomplish this end, the superheater is operated on a fixed volume of air or other combustion supporting gas and the fuel supply is varied to meet temperature requirements and/or varying fluid flow requirements. With the superheater described above, fuel input affects both flame temperature and combustant temperature. Therefore, both radiant heating and convection heating are affected. With the constant volume of air supplied and discharged, temperature response is instantaneous.

Referring to FIGURE 2, a constant volume of air is supplied to fuel burner 14 by a compressed air blower 28. Quantitative control of fuel flow in line 23 is maintained by valve which is controlled by valve drive unit 32.

At the heated fluid discharge end of longitudinally extended heating chamber 12, temperature sensor 34, connected to line 24, measures the temperature of heated fluid. Sensor 34 generates a signal which is delivered over line 36 to temperature controller 38 and, in turn, a signal is delivered over line 40 to valve drive unit 32. The temperature desired for superheated fluid can be selected at temperature controller 38 and differences between measured temperature at sensor 34 and desired temperature input to controller 38 generate responsive signals to raise or lower the fuel input to fuel burner 14.

An excess air type of fuel burner as shown in FIGURE 3 is used. This type of burner may also be referred to as a tempered flame burner. A constant pilot is provided; operation of this type of burner will be obvious from FIGURE 3. In combination with other features of the invention, the burner helps to provide rapid temperature response. For example, when fuel is being added the hottest flame, at burner 14, contacts the fluid in coil 20 shortly after entering the heater when the fluid is relatively low in temperature. This large temperature differential facilitates rapid heat exchange. V

Combustion gases travel as shown in FIGURE 1; heat exchange along the internal surface of the cylindrical space defined by convolutions of coil 20 is primarily due to radiant heating. Along the external surface of the cylinder, heat transfer is due chiefly to convection heating. It can be readily seen that when fuel supply is diminished, flame temperature and the temperature of the products of combustion will diminish. Fluid temperatures change within coil 20 will follow rapidly with heat exchange facilitated by the constant volume of air supplied by compressed air blower 28. Whether heating up or cooling down, heat exchange takes place over the full surface area of the coil because of the coils configuration. In effect, instantaneous temperature response is available by controlling fuel input. This rapid response is especially important when steam flow requirements vary since heating requirements would vary instantaneously with change in the flow rate demand.

Referring to FIGURE 2, fluid under pressure is supplied via line 22. The pressure may be regulated through pressure regulator valve 42. In operation, the pressure is sensed near the point of use of the superheated fluid by pressure sensor 44 which generates a signal which is delivered over line 45 to pressure controller 46. Desired pressure is selected at pressure controller 46. Any differential between measured and desired pressure controls the pressure regulator valve 42.

The present invention can be used for control of superheated steam used in a jet coating control process. Referring to FIGURE 4, galvanized strip 5% is traveling upwardly from a hot-dip coating pot (not shown) between superheated steam nozzles 52 and 54 which are used to control the coating weight of molten galvanize on the strip. It is essential in this environment to maintain instantaneous control of the temperature and pressure of the steam in order to exercise proper coating control for the varying gauges of steel strip being coated. The speed of the line varies with variation in strip gauge and the temperature, pressure, and flow requirements may vary accordingly.

The control features described in relation to FIGURE 2 are employed in this environment, as are various safety controls. For example, nozzles 52 and 54 have regulator valves 56 and 58, respectively. These may be automatically controlled from control panel 60. Pressure and temperature indicator gauges for the entire system may be included in control panel 60. At the supply end of the heat exchange unit 12, a manually operated butterfly valve 62 is provided in line 25. Pilot controls 64 are provided for the constant pilot of burner 14 and flame protection relay 66 is provided for safety reasons. A main gas pressure regulator is provided at 68 and a safety valve is provided at 70.

The above system functions to provide instantaneous control of superheated gas as required to provide temperature selectivity and meet varying flow demands.

superheater structure and methods and apparatus for superheater control which combine to provide rapidresponse temperature selectivity and other contributions to the art have been described. Modifications to and variations of such structure, methods, and apparatus will be possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Independent superheater structure and control apparatus comprising longitudinally extended heating chamber means,

helical coil means, for carrying a fluid to be heated,

having convolutions defining a longitudinally extended cylindrical configuration having its longitudinal axis substantially parallel with the longitudinal axis of the heating chamber means, the helical the helical coil means having a fluid inlet means at one longitudinal end of the heating chamber means and a fluid outlet means at the opposite longitudinal end of the heating chamber means,

fluid suply means connected to the fluid inlet means of the helical coil means for supplying a fluid under pressure to be heated during flow through the helical coil means,

fuel burner means at the longitudinal end of the heating chamber means having the fluid inlet means, the fuel burner means being disposed to discharge gases of combustion along the longitudinal axis with-in the cylindrical configuration formed by the convolutions of the helical coil means,

fuel supply means connected to the fuel burner means including fuel input control means for quantitatively controlling the fuel delivered to the fuel burner means,

combustion supporting gas supply means connected to the fuel burner means and including means for supplying a constant volume of combustion supporting gas to the fuel burner means,

temperature sensing means located at the fluid outlet means to measure fluid temperature and generate a signal in response to such temperature measurement, and

means connecting the temperature sensing means to the fuel input control means to control fuel input in response to temperature measurement.

2. The independent superheater structure and control apparatus of claim I further including pressure sensing means located at the fluid outlet means to measure fluid pressure within the helical coil means and generate a signal in response to such pressure measurement,

fluid supply pressure control means, and

means connecting the pressure sensing means to the fluid supply pressure control means to control fluid supply to the helical coil means responsive'to pressure measurements by the pressure sensing means.

3. The independent superheater structure and control apparatus of claim 1 further including means for selecting a desired fluid temperature, and

temperature regulator means connected between the temperature sensing means and the fuel input con trol means to coordinate measured temperature with desired temperature and regulate fuel input responsive thereto.

4. The independent superheater structure and control apparatus of claim 2 further including means for selecting a desired pressure for fluid delivered from the heating chamber means, and

pressure regulator means connecting the pressure sensing means, the fluid supply pressure control means, and the means for selecting desired fluid pressure to coordinate measured fluid pressure with desired fluid pressure.

5. Method of operating an independent superheater to provide rapid response to selected temperature control, the independent superheater having heating coil means disposed within a heat exchange chamber, a fuel burner means for introducing fuel and combustion supporting gas to the heat exchange chamber, and flue means for discharging the gases of combustion from the heat exchange chamber, comprising the steps of quantitatively controlling supply of combustion supporting gas to the fuel burner means to maintain the amount of combustion supporting gas delivered to the heat exchange chamber at a predetermined and fixed value,

maintaining flue discharge capacity from the heat exchange chamber at a fixed value,

measuring the temperature of fluid after heating in the heat exchange chamber, and

controlling fuel input to the heat exchange chamber to maintain the temperature of fluid delivered from the heat exchange chamber at a desired level, fuel input being controlled automatically in response to fluid temperature measurement.

6. Method of operating an independent superheater to automatically deliver fluid at desired temperature, the independent superheater including heating coil means disposed within a heat exchange chamber, inlet and outlet means for fluid to be heated by the superheater, fuel burner means for combining fuel and combustion supporting gases and discharging gases of combustion into the heat exchange chamber, and flue means for discharging gases of combustion from the heat exchange chamber, comprising the steps of delivering combustion supporting gases to the fuel burner means,

quantitatively controlling supply of combustion supporting gases to deliver a predetermined and substantially constant volume of combustion supporting gases to the fuel burner means,

burning the fuel and combustion supporting'gases to produce gases of combustion,

discharging the gases of combustion into the heat exchange chamber,

maintaining the flue discharge capacity for the heat exchange chamber for gases of combustion substantially constant, 1

measuring the temperature of fluid heated in the heat exchange chamber, and quantitatively controlling fuel delivered to the fuel burner means responsive to temperature measurement of heated fluid to automatically maintain fluid delivered from the heat exchange chamber at a preselected level. 7. The method of claim 6 further including steps for automatically controlling the pressure of fluid heated in the heat exchange chamber to deliver fluid at a preselected level comprising the steps of measuring the pressure of fluid being delivered from the heat exchange chamber after heating, and

controlling the pressure of fluid delivered to the fluid inlet means to :be heated by the chamber in response to measured pressure.

3. Apparatus for delivering superheated steam at selected temperature and pressure for controlling coating Weight of hot-dip coated steel strip by directing the superheated steam onto the strip upon exit from a hot-dip coating bath, comprising longitudinally extended heating chamber means,

coil means for carrying steam to be heated, the coil means being disposed Within the heating chamber means With coil convolutions defining a cylindrical configuration having its longitudinal axis substantially parallel With the longitudinal axis of the heating chamber means,

steam inlet means connected to the coil means at one longitudinal end of the heating chamber means and steam outlet means connected to the coil means at the opposite longitudinal end of the heating chamber means,

steam supply means for delivering steam under pressure to the steam inlet means,

valve means for controlling the pressure of steam delivered to the steam inlet means,

fuel burner means connected to the heating chamber means for discharging gases from combustion of fuel and combustion supporting gases along the longitudinal axis of the coil means in heat exchange relationship with steam in the coil means,

fuel supply means connected to the fuel burner means,

fuel input control means connected to the fuel supply means,

combustion supporting gas supply means and means for controlling delivery of a predetermined and substantially fixed volume of combustion supporting gas to the fuel burner means,

flue discharge means for the heating chamber means having a substantially fixed discharge capacity,

pressure sensing means for measuring pressure of steam heated in the heating chamber means and producing a signal responsive to such pressure measurement,

pressure regulator means, connected to the pressure sensing means and the valve means, for controlling pressure of steam delivered to the fluid inlet means for maintaining the pressure of superheated steam at a preselected level,

temperature sensing means for measuring the temperature of superheated steam from the heating chamber means,

temperature control means connected to the temperature sensing means and the fuel input control means for maintaining the temperature of superheated steam at a preselected level, and

means for delivering superheated steam from the heating chamber means to the hot-dip coating operation at preselected temperature and pressure.

FOREIGN PATENTS 738,662 10/1932 France. 792,747 4/1958 Great Britain.

KENNETH W. SP'RAGUE, Primary Examiner. 

1. INDEPENDENT SUPERHEATER STRUCTURE AND CONTROL APPARATUS COMPRISING LONGITUDINALLY EXTENDED HEATING CHAMBER, MEANS, HELICAL COIL MEANS, FOR CARRYING A FLUID TO BE HEATED, HAVING CONVOLUTIONS DEFINING A LONGITUDINALLY EXTENDED CYLINDRICAL CONFIGURATION HAVING ITS LONGITUDINAL AXIS SUBSTANTIALLY PARALLEL WITH THE LONGITUDINAL AXIS OF THE HEATING CHAMBER MEANS, THE HELICAL THE HELICAL COIL MEANS HAVING A FLUID INLET MEANS AT ONE LONGITUDINAL END OF THE HEATING CHAMBER MEANS AND A FLUID OUTLET MEANS AT THE OPPOSITE LONGITUDINAL END OF THE HEATING CHAMBER MEANS, FLUID SUPLY MEANS CONNECTED TO THE FLUID INLET MEANS OF THE HELICAL COIL MEANS FOR SUPPLYING A FLUID UNDER PRESSURE TO BE HEATED DURING FLOW THROUGH THE HELICAL COIL MEANS, FUEL BURNER MEANS AT THE LONGITUDINAL END OF THE HEATING CHAMBER MEANS HAVING THE FLUID INLET MEANS, THE FUEL BURNER MEANS BEING DISPOSED TO DISCHARGE GASES OF COMBUSTION ALONG THE LONGITUDINAL AXIS WITHIN THE CLYINDRICAL CONFIGURATION FORMED BY THE CONVOLUTIONS OF THE HELICAL COIL MEANS, 